[Ocfs2-devel] [nov 28] question of dlm_get_lock_resource()

[Coly Li]

Hi list,

When I read code of dlm_get_lock_resource(), there is something not clear to me.

 719 lookup:
 720         spin_lock(&dlm->spinlock);
 721         tmpres = __dlm_lookup_lockres_full(dlm, lockid, namelen, hash);
 722         if (tmpres) {
 723                 int dropping_ref = 0;
 724
 725                 spin_lock(&tmpres->spinlock);
 726                 if (tmpres->owner == dlm->node_num) {
 727                         BUG_ON(tmpres->state & DLM_LOCK_RES_DROPPING_REF);
 728                         dlm_lockres_grab_inflight_ref(dlm, tmpres);
 729                 } else if (tmpres->state & DLM_LOCK_RES_DROPPING_REF)
 730                         dropping_ref = 1;
 731                 spin_unlock(&tmpres->spinlock);
 732                 spin_unlock(&dlm->spinlock);
 733
 734                 /* wait until done messaging the master, drop our ref to allow
 735                  * the lockres to be purged, start over. */
 736                 if (dropping_ref) {
 737                         spin_lock(&tmpres->spinlock);
 738                         __dlm_wait_on_lockres_flags(tmpres, DLM_LOCK_RES_DROPPING_REF);
 739                         spin_unlock(&tmpres->spinlock);
 740                         dlm_lockres_put(tmpres);
 741                         tmpres = NULL;
 742                         goto lookup;
 743                 }
 744
 745                 mlog(0, "found in hash!\n");
 746                 if (res)
 747                         dlm_lockres_put(res);
 748                 res = tmpres;
 749                 goto leave;
 750         }

If at line 721 tmpres found from hash, and its state is not DLM_LOCK_RES_DROPPING_REF (dropping_ref
is 0), between line 733 and 748, is it possible to set tmpres->state to DLM_LOCK_RES_DROPPING_REF ?

I don't see any protection for this race, maybe there is something I missed. Can anybody give me a
hint ?

Thanks.
-- 
Coly Li
SuSE PRC Labs